Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
1999-08-26
2003-02-25
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S327000, C148S269000, C148S274000, C148S282000
Reexamination Certificate
active
06524644
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for the treatment of metallic surfaces for the protection of the surface from oxidation and for enhancing its solderability and, more particularly, to treating electronic components such as printed wiring boards (PWB's) containing both copper and gold circuitry to provide a protective coating on the copper before the copper is soldered with the gold features on the substrate not being discolored or otherwise electrically affected by the treatment.
2. Description of Related Art
In the manufacture of metal containing components which are to be soldered, it is necessary to protect the metal from oxidation to enhance its solderability. For convenience the following description will be directed to the manufacture of printed wiring boards (PWB's) or other electronic components having copper circuitry which is to be soldered and where it is essential that the copper not be oxidized or otherwise corroded prior to soldering.
Typically, many such electronic components having copper circuitry thereon also have gold leads or other electrical connections which are generally used to connect the electronic component to another electronic component. Currently however, processes used to protect the copper circuitry prior to soldering deleteriously affect the gold metallurgy on the substrate by staining the gold or otherwise electrically affecting the gold.
The processes used today for protecting copper prior to soldering employ a protective coating deposited on the copper. This coating is used as an alternative to hot air solder leveling (HASL) and other metallic printed circuit board surface finishes. The coating provides protection against copper solderability degradation caused by various process steps in the fabrication process such as exposure to multiple heat cycles during electronic component fabrication for surface mount technology (SMT) and mixed technology PWB assembly.
Generally, copper protective coating systems utilize a number of steps including cleaning, microetching and acid rinsing followed by the formation of a protective coating on the copper using a solution containing a protective forming agent. The protective forming agent is typically an imidazole or benzimidazole derivative and the coating is generally termed an organic solderability preservative (OSP) coating.
A number of patents have issued in this area which have attempted to solve the problems associated with providing a protective coating on copper circuitry.
U.S. Pat. No. 5,658,611 to Ishiko et al. provides an aqueous surface protection composition for PWB's containing a benzimidazole derivative and adjusted to a pH of 1-5 with a salt forming acid of a heavy metal such as copper, manganese and zinc in an amount not higher than 50 ppm.
In U.S. Pat. No. 5,173,130 to Kinoshita et al. a process is disclosed for the surface treatment of copper which comprises immersing the surface of the copper in an aqueous solution containing a benzimidazole compound having an alkyl group of at least three carbon atoms at the 2-position and an organic acid. Similarly, in U.S. Pat. Nos. 5,498,301 and 5,560,785 to Hirao et al. a water-based surface treatment agent used to protect copper on a printed wiring board with excellent heat-resistance and moisture-resistance utilizes as an active ingredient a 2-arylimidazole compound.
In EPA Publication No. EP 0 791 671 to Hirao et al. a surface treating agent for copper is disclosed comprising an aqueous solution containing an imidazole compound or a benzimidazole compound, a complexer and iron ions. It is contended that the surface treating agent forms a chemical film selectively on the surface of copper while forming no film on other metals.
In U.S. Pat. No. 5,362,334 to Adams et al. a composition and process for the surface treatment of metallic surfaces such as copper circuitry on printed circuit boards is disclosed which comprises treating the surface with an aqueous solution comprising a benzimidazole compound having either a halogenated phenyl group, a halogenated benzyl group or a halogenated ethyl phenyl group in the 2-position. In U.S. Pat. No. 5,376,189 to Kukanskis a composition and process are disclosed for the treatment of metallic surfaces such as copper on printed circuit boards which comprises treating the surface with an aqueous solution comprising a benzimidazole compound which has at least one carboxylic or sulfonic acid group directly or indirectly attached to the benzimidazole compound.
Unfortunately, current processes for producing a protective coating on the copper surface still, in varying degrees, deleteriously affect the gold metallurgy on the electronic substrate because it attracts the coating used to coat the copper and causes cosmetic defects in the form of staining and may reduce the conductivity of the gold contact surface.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved method to selectively deposit an organic solderability preservative (OSP) coating on copper surfaces of electronic components such as printed wiring boards to serve as a protective coating to preserve the solderability of the copper surfaces while substantially excluding gold surfaces from attracting the same protective coating and staining the gold and/or affecting the conductivity of the gold.
It is another object of the present invention to provide electronic components such as printed wiring boards made using the method of the invention.
Other advantages of the invention would be readily apparent from the following description.
SUMMARY OF THE INVENTION
In one aspect of the invention the method for the treatment of metallic surfaces to protect the surface from oxidation and for enhancing its solderability and, in particular, to treating electronic components such as printed wiring boards containing both copper and gold circuitry to provide a protective coating on the copper before the copper is soldered with the gold features on the substrate not being discolored or otherwise electrically affected by the treatment has been improved. In the method for the treatment of metallic surfaces for protection of the surface from oxidation for enhancing its solderability the metallic surface is cleaned, optionally etched and then contacted with a solution of an organic solderability preservative material typically a triazole, imidazole or benzimidazole or derivatives thereof whereby an organic solderability preservative protective film or coating is formed on the metallic surface, the improvement comprising:
contacting the metallic surface with a pre-treatment solution prior to contact of the metallic surface with an organic solderability preservative material typically a solution of triazole, imidazole or benzimidazole or derivatives thereof used to provide the organic solderability protective coating, the pre-treatment solution comprising a benzimidazole compound having the formula:
wherein R
1
, R
2
, R
3
, and R
4
are independently selected from the group consisting of hydrogen atoms, substituted or unsubstituted alkyl groups of 1-10 carbon atoms, preferably a lower alkyl of 1-4 carbon atoms, substituted or unsubstituted aryl groups, halogen atoms, alkoxy groups of 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, alkyl amino groups of 1 to 10 carbon atoms, preferably 1-4 carbon atoms, cyano groups, nitro groups and mixtures thereof.
In a preferred aspect of the invention R
1
, R
2
, R
3
, and R
4
are all hydrogen.
The benzimidazole compound used to form the pre-treatment solution is dissolved to form a solution, preferably aqueous, and preferably includes a corrosion inhibitor compound such as an alkanolamine, e.g., a C1-C4 alkanolamine such as triisopropanolamine, and a buffering agent such as a salt like ammonium acetate to stabilize the pH. The solution may be used over a wide range of temperatures typically 70° F. to the boiling point of the solution, typically 70° F. to 120° F., preferably 70°
Enthone Inc.
Senniger Powers Leavitt & Roedel
Talbot Brian K.
LandOfFree
Process for selective deposition of OSP coating on copper,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for selective deposition of OSP coating on copper,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for selective deposition of OSP coating on copper,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3154873